Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/18

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Dr. Mac Culloch on certain products

I exposed a quantity of the pitch to a careful distillation through water. As might be expected from what I described before in the distillation of the tar, this process gave results nearly similar to the former. The oily matter differed in being of a brown colour and in having a greater specific gravity, and much less acid was produced; the residuum was charcoal. The whole process of distillation appears, therefore, to be a decomposition by which the pitchy substance is converted into oil, acetic acid, ammonia and charcoal.

I proceeded next to examine the oil. It has a violently pungent taste and smell. It is scarcely heavier than water; so that it sinks in that fluid with difficulty, leaving generally some drops on the surface. It is perfectly soluble in alcohol, in ether, in caustic alkali, in olive oil, and in linseed oil. It will unite neither to naphtha, nor to the recent essential oils, but is soluble in the old ones. From these properties, it belongs to the class of the essential oils, but exhibits at the same time other qualities by which it is distinguished from the whole of them.

Having thus examined the most remarkable chemical properties of this substance, it will not be irrelevant to point out its differences from and its analogies with those substances which it most resembles, namely resin and the bitumens. Resin, as is well known, is eminently soluble in all the substances in which this is dissolved, and also in those with which this refuses to unite, even naphtha. But the general analogy between essential oil, turpentine and resin, is so close to that of the three substances which I have described, that it will not perhaps be superfluous here to make some remarks on the nature of common resin and the substances connected with it, pitch, tar, turpentine and essential oil, as their history will also illustrate that of the substance I am describing, and as it appears, like that of the bitumens, to have been somewhat mistaken.